Method of operating a cement kiln

ABSTRACT

A new cement kiln and method of heating cement kiln feed is described which involves providing a plurality of circumferential, elongated, lifting vanes near the gas exit end of the kiln. The edge of the last row of lifters is within three feet of the end of the kiln chain system and the double rows of lifters occupy an area representing the upper 2 to 10 percent of the total kiln length. The lifters drop kiln feed through the kiln gases as the gases pass from the lower to the upper end of the kiln and heat is transferred from the gases to the solids. A considerable reduction in the kiln exit gas temperature is accomplished using this method of imparting heat to kiln feed and a reduction in the quantity of fuel needed to supply heat to the the kiln is also realized.

United States Patent Kistler Sept. 5, 1972 [7 2] Inventor: Richard P. Kistler, Zanesville, Ohio [73] Assignee: PPG Industries, Inc., 2, Pittsburgh,

[22] Filed: Dec. 21, 1970 [21] Appl. No.: 99,811

, [52] US. Cl. ..263/53 R, 263/33 R [51] Int. Cl. ..C04b 7/44 [58] Field of Search ..263/32 R, 33 R, 53 R [56] References Cited UNITED STATES PATENTS 3,563,521 2/1971 Olsen ..263/33 R 2,104,040 1/1938 Hurt ..263/33 R 2,188,798 1/1940 Smith ..263/33 R 3,152,796 10/1964 Ramstack, Jr. ..263/33 R Primary Examiner-John J. Camby Att0mey-Chisholm & Spencer [57] ABSTRACT A new cement kiln and method of heating cement kiln feed is described which involves providing a plurality of circumferential, elongated, lifting vanes near the gas exit end of the kiln. The edge of the last row of lifters is within three feet of the end of the kiln chain system and the double rows of lifters occupy an area representing the upper 2 to 10 percent of the total kiln length. The lifters drop kiln feed through the kiln gases as the gases pass from the lower to the upper end of the kiln and heat is transferred from the gases to the solids. A considerable reduction in the kiln exit gas temperature is accomplished using this method of imparting heat to kiln feed and a reduction in the quantity of fuel needed to supply heat to the the kiln is also realized.

4 Claims, 3 Drawing Figures PATGNTEDSEP 5 m2- FIO.1

Ohm-$3 2 ATTORNEYS METHOD OF OPERATING A CEMENT KILN BACKGROUND OF THE INVENTION In the manufacture of cement it is conventional to utilize brick lined kilns to prepare the cement clinker. Typically shale and limestone are fed to one end of an inclined kiln and hot gases produced by a burner located at the bottom end of the kiln opposite the feed end heat the shale and limestone to a sintering temperature during their travel through the kiln to form a cement clinker. The clinker is subsequently mixed with gypsum and crushed to proper size to produce a commercial grade Portland cement. In this operation large quantities of fuel are employed in the kiln burner whether it be an oil, gas or coal burner. This fuel consumption represents a considerable cost and is in part excessive because of the inefficient heat transfer from kiln gases to kiln solids.

THE PRESENT INVENTION In accordance with the instant invention an extremely efficient system is provided for the transfer of heat from kiln gases to kiln solids which has resulted in a substantial reduction in the quantity of fuel required to produce a cement clinker at a given feed rate and residence time of kiln solids in a cement kiln. That heat transfer superior to that previously possible has been achieved has also been demonstrated by the instant invention in the substantial lowering of kiln gas temperatures that has been observed at the solids feed end of the cement kiln using this invention.

As practiced, in broad terms the instant invention involves providing at the upper end of a cement kiln an atmosphere of feed particles through which hot kiln gases must pass prior to exiting from the kiln. This atmosphere of kiln solids in the feed end of the kiln is provided by continuously showering kiln solids through the gas zone in this area from a plurality of solids distribution means. The solids distributors continuously rain solid particulates from the upper surfaces of the kiln at the inlet end to the lower surfaces of the kiln at the inlet end. Arrangement of the distributors is such that the kiln solids at the feed end of the kiln are continuously being passed through the kiln gases in that area of the kiln thus creating an atmosphere of particles through which hot kiln gases must flow in their path to the kiln exit. This atmosphere of kiln particulates is provided in the kiln at the inlet end and represents at least 2 percent of the total gas volume of the kiln and preferably 2.5 to percent of the kiln volume. While more than 10 percent of the volume can be employed, this usually is not necessary to achieve optimum heat transfer and adds considerably to the overall expense of the method.

The invention in its various aspects will be more readily understood from the ensuing description taken in conjunction with the accompanying drawing in which:

FIG. 1 shows a longitudinal view of a cement kiln with a wall broken away to show the interior;

FIG. 2 is a cross section of FIG. 1 take along lines AA and showing particulate distribution during operation; and

FIG. 3 is an enlarged perspective view of a section taken at lines B-B of FIG. 2.

Turning to the drawing, and FIG. 1 in particular,

there is shown a cement kiln 1 provided with a plurality of solids distributors or vanes 2. Vanes 2 are supported by a plurality of base supports 3 which are affixed to the kiln wall in an appropriate manner for example by welding. The kiln l is lined with a suitable refractory brick 4 to protect the kiln shell from damage due to heat and/or corrosion. High zirconia content brick is a suitable refractory for this purpose. In FIG. 3 the base support member 3 is shown affixed to the kiln shell by a continuous weld 5 and this forms the preferred mode of supporting the distributors 2 in their position as shown. The base of the distributors 2 runs parallel to the longitudinal axis of the kiln and rests firmly on the refractory bricks 4. It is preferred to employ at least three support members 3 for each distributor 2. The base support members 3, as shown in FIG. 3, are partially covered by the refractory bricks 4 and normally will have a small depth of grout over the weld or other form of attachment to the kiln shell used.

The distributors 2 are preferably formed so that the major portion of the unit is perpendicular to the long axis of the cement kiln. Near the free end (the end opposite the base resting on the brickwork) the distributors 2 are bent into two sharp angles from the perpendicular portion of the distributors. The first bend 2a preferably forms a 45 angle with a line drawn perpendicular to the major portion of the distributors 2 and the second bend 2a preferably forms a angle with a line drawn in the same manner. These bends 2a and 2b in the distributors 2 help in maintaining material on the distributors 2 during rotation of kiln 1. Of the total extension of the distributors 2 from the kiln bricks 4 to the interior of the kiln the curved or bent portion of the distributor represents 12 to 25 percent, preferably about 15 to 18 percent. The distributors 2 are bent so that the bends point in the direction of kiln rotation.

The longitudinal dimension of the distributors 2 is such that a double row of these elements having a slight (1 inch to 6 inches) overlap at their edges shower kiln feed through an area representing 2 to 10 percent of the kiln volume. In a typical application of the invention involving a 450 foot kiln, 14.5 feet in diameter, the distributors 2 are 6 feet in length and have an effective length of 12 inches into the kiln from the surface of the bricks 4. As shown in FIG. 1 the first row of distributors overlap the second row slightly (2 inches in this embodiment). Thus, the distributors 2 represent an effective length of 11 feet 10 inches. On a volume basis, ignoring the volume occupied by the metal used to form the distributors 2, they effectively shower particulates through the kiln gas space to present an atmosphere of particulates therein representing about 2.5 percent of the total kiln volume. This zone of heavy particulates is located at the inlet end of the kiln. In this operation it is preferred that the row of distributors nearest to the inlet end of the kiln have their uppermost ends positioned about 3 feet inside the end of the kiln.

In general the distributors 2 thus occupy about 2 percent to about 10 percent of the kiln length and in showering particulates 6 through the kiln gases at the inlet end present a volumetric amount of particulate which occupies 2 to 10 percent of the kiln volume. While particulates, due to rotation of the kiln and gas mixing, are present in all areas of the kiln, it. will be found that the area bounded by the distributors 2 has an atmosphere of high solids density compared to the remaining areas of the kiln. The gas flow through this area of dense particulates rapidly transfers heat from the hot combustion gases to the particulates. Thus, in the example given above of the 450 foot kiln, 14.5 feet in diameter with the lifters occupying 2.5 percent of the kiln length and providing a dense particulate zone of 2.5 percent of the total kiln volume, it was found that the kiln gas temperature at the inlet end of the kiln was effectively lowered from 575 F. to 425 F. The total volume of fuel used was lowered by percent during this period of testing which was conducted for a period of 7 months. The lower temperature and reduced fuel consumption indicate that heat transfer from the gases to the particulates at the inlet end of the kiln were excellent and heat utilization in the kiln was markedly improved with the use of the instant invention.

The process and apparatus described herein can be utilized in either a dry feed cement kiln or one in which a slurry feed is employed. The kiln described above used a slurry feed.

The solids distributors 2 used in conjunction with their supports 3 have been found to be quite sturdy. In the practice of the invention these distributors are placed preferably equidistant from each other around the circumference of the kiln. The two rows employed are staggered as shown in FIG. 1 for maximum distribution of material through the kiln gas. While two rows of distributors, each having eight distributors, are shown in the drawing, this is for illustrative purposes only. If desired, more rows can be employed and more distributors can be used per row. The important consideration is that at least 2 volume percent of the kiln near the inlet end be employed as an area having a dense particulate atmosphere exposed to kiln gases prior to their departure from the kiln.

The cement kilns in which the invention is practiced are typically inclined from the feed end to the discharge end and rotate at slow speeds from one-third to 6 revolutions per minute. Kilns such as those described on pages 159-162 of the. book Industrial Chemistry", Riegel, 4th Edition, are illustrative of the type furnaces in which the invention may be practiced. As shown the kilns are fed at the high end with either a slurry of limestone and shale or dry limestone and shale. The hot combustion gases are introduced into the interior of the kilns at the low end and pass through the length of the kiln, i.e., in a countercurrent direction to the feed. These gases ultimately leave the kiln at the solids inlet end.

While the invention has been described with reference to certain specific illustrative embodiments, it is not intended to be so limited except insofar as appears in the accompanying claims.

lclaim:

1. In the method of operating an inclined rotary cement kiln wherein shale and limestone feed is introduced into the feed inlet end of the kiln and hot gas is passed upwardly through the kiln countercurrent thereto, the improvement which comprises establishing a zone of high feed density within and near the feed inlet end of the kiln wherein the feed is dispersed at a higher density than elsewhere in the kiln, said zonere rese ting from.2 to 10 perc nt of the tgtal interna ki 11 v0 ume, passing hot gas t rough sal zone, an

removing cement clinker from the feed discharge end of the kiln.

2. The process of claim I wherein the zone of high feed density is established by lifting the feed solids with a plurality of lifting vanes located circumferentially around the internal wall of the kiln within said zone.

3. In the method of operatingan inclined rotary cement kiln wherein a feed of shale and limestone solids is introduced into the feed inlet end of the kiln and hot kiln gas is passed upwardly through the kiln countercurrent thereto, the improvement which comprises improving heat transfer between the kiln gas and feed solids by establishing a zone of high feed density within and adjacent to the feed inlet end of the kiln, the feed being dispersed throughout the zone at a higher density than elsewhere in the kiln and wherein said zone represents from 2 to 10 percent of the total internal kiln volume, passing hot kiln gas through said zone, and removing cement clinker from the feed discharge end of the kiln.

4. The process of claim 3 wherein the zone of high feed density is established by lifting the feed solids with a plurality of lifting vanes located circumferentially around the internal wall of the kiln within said zone. 

1. In the method of operating an inclined rotary cement kiln wherein shale and limestone feed is introduced into the feed inlet end of the kiln and hot gas is passed upwardly through the kiln countercurrent thereto, the improvement which comprises establishing a zone of high feed density within and near the feed inlet end of the kiln wherein the feed is dispersed at a higher density than elsewhere in the kiln, said zone representing from 2 to 10 percent of the total internal kiln volume, passing hot gas through said zone, and removing cement clinker from the feed discharge end of the kiln.
 2. The process of claim 1 wherein the zone of high feed density is established by lifting the feed solids with a plurality of lifting vanes located circumferentially around the internal wall of the kiln within said zone.
 3. In tHe method of operating an inclined rotary cement kiln wherein a feed of shale and limestone solids is introduced into the feed inlet end of the kiln and hot kiln gas is passed upwardly through the kiln countercurrent thereto, the improvement which comprises improving heat transfer between the kiln gas and feed solids by establishing a zone of high feed density within and adjacent to the feed inlet end of the kiln, the feed being dispersed throughout the zone at a higher density than elsewhere in the kiln and wherein said zone represents from 2 to 10 percent of the total internal kiln volume, passing hot kiln gas through said zone, and removing cement clinker from the feed discharge end of the kiln.
 4. The process of claim 3 wherein the zone of high feed density is established by lifting the feed solids with a plurality of lifting vanes located circumferentially around the internal wall of the kiln within said zone. 